This invention relates to a device for through-flow process of web-form fabric, fleece, paper, tissue or the like with a fluid but especially gaseous, processing medium circulated throughout the entire device by a fan, with a permeable, e.g. a screen drum, traversed from the exterior to the interior and placed in a vacuum and having non-perforated walls at the ends, said drum serving as a transport element for the web-form material, which, to form the processing medium baffle chamber in front of a processing chamber, has associated with its a baffle cover with perforations, axially parallel to the drum, said perforations being arranged crosswise over the working width of the drum, the processing medium permeability of said cover being less than that of the drum.
A screen drum design of this type is known. The baffle cover is required to distribute the recirculated fluid upstream from the processing chamber, in which the screen drum is rotatably mounted, uniformly over the working width of the drum, so that it then flow perpendicularly to the surface of the screen drum, in equal air flow volumes to the screen drum. This produces a uniform temperature distribution over the working width of the screen drum. The jacket or cylindrical casing for the screen drum can be made from a piece of perforated sheet metal over which a braided screen can be wrapped to even out the air flow through the perforations. The air permeability of this sheet metal jacket, however, is limited to approximately 45% of the total surface of the drum because of the ribs between the holes or perforations required for stability of the jacket. Drums whose jackets are composed of sheet metal strips extending radially are better. These drums, which are up to 96% permeably, are used especially for drying paper and fleece.
When such screen drum designs are used, material webs of different widths must be handled. In order to limit the air flow to the width of the material web, the marginal areas of the drum which are not covered by the web of material to be treated can be covered in known fashion by an air-impermeable cloth. This method is too cumbersome, however, especially when the working width of the material changes rapidly It is also known from DE-OS 19 00 496 to limit the inflow area to the working width by using walls which are located outside the screen drum and which form a seal with the baffle cover. A design according to DE-OS 16 35 263 is better, in which the adjustment of the working width of the screen drum is achieved by walls or cover panels on the inside of the screen drum. This adjustability, however, is limited to only a small portion of the entire working width, and in particular, only the marginal areas can be covered in order to be able to use the middle of the drum. It is not good if, for example, only one marginal strip at the outer edge of the screen drum is to remain open, but the remainder of the screen drum is to be covered.
Such a case occurs, for example, when drying fleece, paper or tissue which, when production begins, approach the continuous system at the same very high speed of 600 m/sec. or more, for example. Production of these goods, however, cannot begin over the entire working width of 2 to 5 m because the web must first be threaded around the many rolls and through the various processing assemblies in the continuous system. At the high feed rate, this is only possible with a narrow strip which must run on the operating side of the continuous system. But this narrow strip must likewise emerge dry from the dryer, and hence solidified, because otherwise the goods cannot be handled, at least they cannot be threaded into the system.
Covering the working width of the screen drum except for this narrow strip, however, is not possible with known devices so that, in the past, the industry has been starting with the entire working width and drying the web as required. Then, however, the web is cut lengthwise, leaving a narrow remainder, while the wide part of the web is sent into the basement as scrap, so that only the remaining narrow strip can be threaded into the system. This method of beginning production consequently involves considerable losses. It is not possible to produce and dry only the narrow strip because when the entire working width of the drum is open, the strip will not dry on the drum. The air leakage is too great for effective drying to be possible in the heat treatment chamber. Consequently, the narrow, non-presolidified strip could not be manipulated after passing through the heat treatment device. The strip does not have the necessary strength, and it tears.